The term “automatic control equipment” is used hereinafter to denote a programmable logic controller, a monitoring/control station, a digital control, or any automatic control module that can contain and run an application program making it possible to monitor/control to an automatic control application, notably like a variable speed drive or a logic module.
Automatic control equipment comprises a central processing unit (CPU) and at least one input/output module providing the link between the central processing unit and sensors and preactuators of the automatic control application to be controlled.
Normally, automatic control equipment such as a programmable logic controller is modular in construction, that is, it consists of several modules that intercommunicate via a backplane bus. A programmable logic controller typically includes a power supply module for supplying the other modules with the various voltages via the backplane bus, a rack for mechanically fixing the modules and supporting the backplane bus to which the modules are electrically connected, and a central processing unit module. The central processing unit module includes a microprocessor and storage means storing a manufacturer program (“firmware”) expressed in a language specific to the manufacturer of the automatic control equipment, an application program (also called user program) for handling the monitoring and/or control of an automatic control application or of a part of an automatic control application by means of inputs/outputs driven by the application program, and data, in particular images of the states of the input/output modules. The programmable logical controller also includes several input/output modules of various types according to the process to be controlled and one or more modules for communicating with communication networks (Ethernet, etc) or control interfaces such as screen, keyboard, etc.
In order to manage and synchronize the various automatic control tasks, the central processing unit of the automatic control equipment comprises a clock. In the prior art, this clock is a conventional RTC (“Real Time Clock”) hardware component which the microprocessor accesses to manage the time in the automatic control equipment. When current is interrupted, a battery is used to maintain time management for the duration of the interruption. However, this type of time management presents certain drawbacks listed below:                since the RTC hardware component is external, access to it is particularly slow,        The standard RTC components are limited to one second of resolution. The use of an RTC component having a resolution less than a second would lead to higher consumption and generate higher cost.        The time-related objects managed by the manufacturer program (for example, a timer) are not synchronized with the RTC hardware component.        
The U.S. Pat. No. 6,603,365 notably proposes replacing the battery with a capacitor. However, the drawback associated with the slowness of access is unresolved.
The aim of the invention is to propose a method and a system for managing time in automatic control equipment in which the current interruptions are controlled with no damage and in which the time information is consistent, presents sufficient resolution and can be quickly recovered.